In a medium bowl, whisk the eggs, cream or milk, kosher salt and pepper. Sprinkle the Gruyere cheese on top of the potato mixture in the skillet. Carefully pour the egg mixture over the top.
Bake for 10-15 minutes or until the eggs are set. Garnish with the sliced green onions.
Recipe by Sunflower Supper Club at https://sunflowersupperclub.com/prosciutto-gruyere-frittata/